The purpose of this project is to study the action of fluoride in various biological tests used to detect clastogenic or mutagenic substances. To date fluoride has been examined in tests used to detect mutagens and found to be non-mutagenic. No effects on chromosome structure were noted in animals given widely different levels of fluoride. DNA repair after X-ray treatment was unchanged by fluoride. No genetic effects of fluoride were noted in a recessive lethal test of fluoride on Drosophila. The data indicate that fluoride has no mutagenic activity. Reports of fluoride's action on the metabolism and growth of cells are being monitored and where appropriate, related studies are undertaken. The changes in major dibasic cation constituents of culture media produced by precipitation of insoluble fluoride salts does not increase mutagenesis in mouse lymphoma cells in culture.